= Awk Patterns =

The core syntax of `awk(1p)` is `pattern { action }`. This page describes '''patterns'''.

<<TableOfContents>>

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== Regular Expressions ==

'''Regular expressions''' are essential to `awk(1p)`. They are a builtin type and are expressed as strings delimited by forward slashes (`/`).

An entire record can be matched against a regular expression as:

{{{
/^[0-9]+ / { print $2 }
}}}

A variable or field can be matched against a regular expression as:

{{{
if ($1 ~ /^[0-9]+$/) { print $2 }
}}}

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== Begin and End ==

The special patterns '''`BEGIN`''' and '''`END`''' are for initialization and clean-up actions.

To initialize a variable that will be referenced in a program, try:

{{{
BEGIN { ansi_reset="\033[0m"; }
}}}

To count the number of records (i.e. lines) in a file, try:

{{{
END { print NR }
}}}

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== Empty Patterns ==

An empty pattern matches every line. This can be written in one of two ways:

{{{
{ print "No pattern at all" }
// { print "Blank regexp pattern" }
}}}



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